Spray application manual
31 January 2025
Module 2: Product requirements
2.1: Getting the pesticide to where it works
Published 24 January 2025 | Last updated 20 January 2025
Most farm chemicals work by affecting a particular mechanism within the target. Usually this involves disrupting or blocking a particular biochemical pathway within a plant or target pest.
The particular mechanism or biochemical pathway that the pesticide or herbicide affects is the basis for the mode of action group it is assigned to. This means that herbicides or pesticides that belong to the same mode of action group affect the same mechanism or biochemical site of activity within target pests or weeds.
Target pests or weeds may respond in a similar way to products from the same mode of action group, which is the basis for many resistance mechanisms. However, there are many things that can affect a product’s ability to get to the site within the pest or plant where it has a biological effect.
For example, with a foliar application of a herbicide, the condition of the plant at the time of spraying, as well as the plant’s response to the environment after spraying, can have a large impact on the ability of the product to enter the plant, and to subsequently move within the plant to the actual target site where it produces the biological response.
Target, Timing and Technique
18 December 2024An introduction to Target, Timing & Technique. Another video for GRDC's Spray Application GROWNOTES™ series.
Bill Gordon: There are a number of factors that will influence the outcome of any spray job. These factors take into account the target itself, the condition it's in, is it susceptible, is it going to take up the product, is it going to translocate it, your choice of adjuvant, which plays a big role, and whether the product can get into the plant quickly or not and how well it will be taken up. But also, we're thinking about what the product does when it hits a target. We're talking about translocation here.
Some products, when they land on the plant, will stay predominately on the surface. They might be things like protectant fungicides or some insecticides. Others will move into the leaf tissue and that's where they stay. Others can move upwards and outwards like many fungicides, some can move down in the plant, and how that product translocates within the plant has a big impact on your choice of application volume, so what sort of coverage you need. For instance, if the product only moves upwards and outwards, we may need to get spray right down through the canopy if that's where we need control.
So this chapter talks about target, timing, translocation, and all those factors that affect the outcome of the job, which will help growers with planning things like droplet size and application volume to get the best out of the situation.
Dose transfer
The process of getting the product from the spray tank to the actual site within the plant or pest where it impacts on the biochemical pathway is often referred to as ‘dose transfer’.
For a successful dose transfer to occur many things must come together.
The application equipment must be right, the conditions must be suitable, the target weed or pest must be susceptible and the product must be able to get onto or into the target and then move to the site within the pest or weed where the product does its job.
The steps involved in getting a herbicide to the target site within a plant are summarised in Table 1.
Factors involved in getting herbicide to the target
Dose transfer can be broken into three general processes:
landing the droplets – droplet formation, deposition and retention;
uptake and translocation of the chemical; and
the biological effect.